Image reading apparatus for reading images formed by a light transmission

Abstract

An illuminator for applying light to an image, a reader for photoelectrically reading the light applied image, an amplifier for amplifying an analog signal outputted from the reader, an A/D converter for converting an analog signal outputted from the amplifier into a digital signal, a logarithmic transformer for logarithmically transforming the digital signal outputted from the A/D converter, a first controller for changing the logarithmic transformation of the logarithmic transformer, and a second controller for changing the gain of the digital signal in accordance with a change of the logarithmic transformation characteristic caused by the first controller.

I claim: 
     
       1. An image reading apparatus comprising: light applying means for applying light to an image;   reading means for photoelectrically reading the image to which light is applied by said light applying means;   amplifying means for amplifying an analog signal outputted from said reading means;   A/D converting means for converting the analog signal outputted from said amplifying means into a digital signal;   logarithmic transformation means for logarithmically transforming said digital signal outputted from said A/D converting means;   first changing means for changing a logarithmic transformation characteristic of said logarithmic transformation means; and   second changing means for changing a property of said digital signal as it is inputted into said logarithmic transformation means, in accordance with a change of the logarithmic transformation characteristic caused by said first changing means, wherein said property is a voltage level.   
     
     
       2. An image reading apparatus according to claim 1, wherein said second changing means changes a reference voltage of said A/D converting means, thereby changing the voltage of said digital signal. 
     
     
       3. An image reading apparatus according to claim 1, wherein said second changing means changes a light amount output by said light applying means. 
     
     
       4. An image reading apparatus according to claim 1, wherein said second changing means changes an amplification factor of said amplifying means. 
     
     
       5. An image reading apparatus according to claim 1, wherein said reading means includes a charge storage type sensor, and said second changing means changes a storage time of said charge storage type sensor. 
     
     
       6. An image reading apparatus according to claim 1, wherein said reading means reads a film to read the image. 
     
     
       7. An image reading apparatus comprising: illuminating means for illuminating a film;   reading means for photoelectrically reading an image recorded in the film illuminated by said illuminating means;   amplifying means for amplifying an analog signal outputted from said reading means;   converting means for converting the analog signal outputted from said amplifying means into a digital signal;   transformation means for logarithmically transforming the digital signal outputted from said converting means;   first changing means for changing a logarithmic transformation characteristic of said transformation means in accordance with a density range of the image recorded in the film; and   second changing means for changing a property of said digital signal as it is inputted into said logarithmic transformation means in accordance with a change of the logarithmic transformation characteristic caused by said first changing means, wherein said property is a voltage level.   
     
     
       8. An image reading apparatus according to claim 7, wherein said second changing means changes a reference voltage of said converting means, thereby changing the voltage of said digital signal. 
     
     
       9. An image reading apparatus according to claim 7, wherein said second changing means changes a light amount output by said illuminating means. 
     
     
       10. An image reading apparatus according to claim 7, wherein said second changing means changes an amplification factor of said amplifying means. 
     
     
       11. An image reading apparatus according to claim 7, wherein said reading means includes a charge storage type sensor, and said second changing means changes a storage tine of said charge storage type sensor. 
     
     
       12. An image reading apparatus comprising: light applying means for applying light to an image;   reading means for photoelectrically reading the image to which light is applied by said light applying means;   amplifying means for amplifying an analog signal outputted from said reading means;   A/D converting means for converting the analog signal outputted from said amplifying means into a digital signal;   logarithmic transformation means for logarithmically transforming said digital signal outputted from said A/D converting means;   first changing means for changing a logarithmic transformation characteristic of said logarithmic transformation means; and   second changing means for changing a property of said digital signal as it is inputted into said logarithmic transformation means, in accordance with a change of the logarithmic transformation characteristic caused by said first changing means, wherein said second changing means changes an amplification factor of said amplifying means.   
     
     
       13. An image reading apparatus comprising: light applying means for applying light to an image;   reading means for photoelectrically reading the image to which light is applied by said light applying means;   amplifying means for amplifying an analog signal outputted from said reading means;   A/D converting means for converting the analog signal outputted from said amplifying means into a digital signal;   logarithmic transformation means for logarithmically transforming said digital signal outputted from said A/D converting means;   first changing means for changing a logarithmic transformation characteristic of said logarithmic transformation means; and   second changing means for changing a property of said digital signal as it is inputted into said logarithmic transformation means, in accordance with a change of the logarithmic transformation characteristic caused by said first changing means, wherein said reading means includes a charge storage type sensor, and said second changing means changes a storage time of said charge storage type sensor.   
     
     
       14. An image reading apparatus comprising: illuminating means for illuminating a film;   reading means for photoelectrically reading an image recorded in the film illuminated by said illuminating means;   amplifying means for amplifying an analog signal outputted from said reading means;   converting means for converting the analog signal outputted from said amplifying means into a digital signal;   transformation means for logarithmically transforming the digital signal outputted from said converting means;   first changing means for changing a logarithmic transformation characteristic of said transformation means in accordance with a density range of the image recorded in the film; and   second changing means for changing a property of said digital signal as it is inputted into said logarithmic transformation means in accordance with a change of the logarithmic transformation characteristic caused by said first changing means, wherein said second changing means changes an amplification factor of said amplifying means.   
     
     
       15. An image reading apparatus comprising: illuminating means for illuminating a film;   reading means for photoelectrically reading an image recorded in the film illuminated by said illuminating means;   amplifying means for amplifying an analog signal outputted from said reading means;   converting means for converting the analog signal outputted from said amplifying means into a digital signal;   transformation means for logarithmically transforming the digital signal outputted from said converting means;   first changing means for changing a logarithmic transformation characteristic of said transformation means in accordance with a density range of the image recorded in the film; and   second changing means for changing a property of said digital signal as it is inputted into said logarithmic transformation means in accordance with a change of the logarithmic transformation characteristic caused by said first changing means, wherein said reading means includes a charge storage type sensor, and said second changing means changes a storage time of said charge storage type sensor.   
     
     
       16. An image reading apparatus comprising: light applying means for applying light to an image;   reading means for photoelectrically reading the image to which light is applied by said light applying means;   amplifying means for amplifying an analog signal outputted from said reading means;   A/D converting means for converting the analog signal outputted from said amplifying means into a digital signal;   logarithmic transformation means for logarithmically transforming said digital signal outputted from said A/D converting means;   first changing means for changing a logarithmic transformation characteristic of said logarithmic transformation means; and   second changing means for changing a voltage level of said digital signal as it is inputted into said logarithmic transformation means, in accordance with a change of the logarithmic transformation characteristic caused by said first changing means, wherein said second changing means changes the voltage level by controlling at least one of said light applying means, said reading means, said amplifying means and said A/D converting means.   
     
     
       17. An image reading apparatus according to claim 16, wherein said second changing means changes the voltage level of the digital signal by controlling a reference voltage of said A/D converting means. 
     
     
       18. An image reading apparatus according to claim 16, wherein said second changing means changes the voltage level of the digital signal by controlling a light amount output by said light applying means. 
     
     
       19. An image reading apparatus according to claim 16, wherein said second changing means changes the voltage level of the digital signal by controlling an amplification factor of said amplifying means. 
     
     
       20. An image reading apparatus according to claim 16, wherein said reading means includes a charge storage type sensor and said second changing means changes the voltage level of the digital signal by controlling a storage time of said charge storage type sensor. 
     
     
       21. An image reading apparatus according to claim 16, wherein said reading means reads a film to read the image. 
     
     
       22. An image reading method comprising the steps of: applying light to an image;   photoelectrically reading the image to which light is applied;   amplifying an analog signal outputting in said reading step;   converting the amplified analog signal into a digital signal;   logarithmically transforming the digital signal to output a resultant signal as an image data signal;   changing a logarithmic transformation characteristic used in said logarithmic transforming step, in accordance with the image to be read; and   changing a property of the digital signal to be logarithmically transformed, in accordance with a change of the logarithmic transforming characteristic.   
     
     
       23. A method according to claim 22, wherein the property of the digital signal to be logarithmically transformed is changed by changing a reference voltage used in converting the analog signal into the digital signal. 
     
     
       24. A method according to claim 22, wherein the property of the digital signal to be logarithmically transformed is changed by changing an amount of light applied to the image. 
     
     
       25. A method according to claim 22, wherein the property of the digital signal to be logarithmically transformed is changed by changing an amplification factor of the analog signal outputted in said reading step. 
     
     
       26. A method according to claim 22, wherein the property of the digital signal to be logarithmically transformed is changed by changing a charge storage time in said photoelectric reading step.